The field of the present invention is control systems for hydraulic motorcycle brakes.
In a conventional motorcycle brake apparatus, a load sensor installed on an upper end of a rear cushion detects load on the motorcycle, based on which an oil pressure is generated. Based on the oil pressure, a characteristic of a pressure control valve is varied to automatically adjust brake force distribution between the front and rear wheels to increase or decrease a rear-wheel brake force as the live load increases or decreases according to, for example, the number of persons riding the motorcycle. Reference is made to Japanese Utility Model Laid-open No. Hei-3-122991. With the conventional motorcycle brake apparatus mentioned above, however, the brake force distribution characteristic between the front and rear wheels is determined unilaterally by the load, disallowing a rider to select a desired brake force distribution characteristic.
A conventional brake apparatus for motorcycles simultaneously generates braking force at a front-wheel brake section and a rear-wheel brake section through either or both a hand-operated lever-system brake and a foot-operated pedal-system brake. Reference is made to Japanese Patent Application Laid-open No. S56-154378. With the conventional constitution, the ratio of the brake force distribution to the front and rear wheels is generally characterized, with the lever-system brake section, by the rear-wheel brake force BFR gradually increasing as the front-wheel brake force BFF increases as indicated by the curve A in FIG. 22 and, with the pedal-system brake section, by the curve B in the same figure. In the case of simultaneously distribution of brake force to the front and rear wheels through the lever and pedal, initiating operation of the pedal while the lever is being operated adds a pedal-brake force to a lever-brake force. This combined operation results in a rapid rise from an operation start point f.sub.1 as indicated by curve B.sub.1. This characteristic operation makes a smooth brake operation difficult. In this case, a rising angle .THETA. equal to the rising angle .THETA. in a solo operation of the pedal is added to the rising angel of the curve A resulting from solo operation of the pedal.
A motorcycle brake apparatus is known in Japanese Utility Model Laid-open No. Hei-3-120286 which has a secondary master cylinder to be operated by a brake reaction force provided by a primary brake cylinder. Secondary brake cylinders are operated by brake oil pressure provided by the secondary master cylinder. A primary master cylinder is operated by a brake operator. An auxiliary oil path transmits a brake oil pressure from the primary master cylinder to the secondary master cylinder. A valve which opens or closes the auxiliary oil path to select either brake oil pressure generated by the secondary master cylinder or brake oil pressure generated by the primary master cylinder transmits the selected brake oil pressure to the secondary brake cylinders. If the brake oil pressure generated by the primary master cylinder is greater than that generated by the secondary master cylinder, the pressure from the primary master cylinder is transmitted from the auxiliary oil path through the secondary master cylinder to the secondary brake cylinders. If the brake oil pressure generated by the secondary master cylinder is greater than that generated by the primary master cylinder, the pressure from the secondary master cylinder is transmitted to the secondary brake cylinders by closing the auxiliary oil path. However, if the brake oil pressure generated by the primary master cylinder is roughly the same as the brake oil pressure generated by the secondary master cylinder, the pressure selector valve may intermittently open and close at short intervals.